It is beneficial for a pilot to be aware of the surroundings by looking outside the cockpit windows while still monitoring the aircraft operational status. More generally, in any type of vehicle operations, it is beneficial for the operator to have enhanced situational awareness. Returning to the example of aircraft operations, traditionally, pilots have relied on the cockpit display screens which are fixed in locations and orientations relative to the pilot's seat. Even with the most recent head-up display (HUD) avionics that allow the pilot looking up while still receiving the electronic information from the avionics display units, when the pilot turns his/her head away from the location of the avionics display units, the flight information is not provided for their attention. More generally, in any vehicle operation where the operators attention needs to be focused on a display unit, even momentary movement of the head away from that display may result in missed information.
As the operation of vehicles becomes more complex, such as the aforesaid example of airplanes, it is preferable that the vehicle operator, e.g., the flight crew, be attentive and receives information in a timely and portable manner to ensure proper operation. One means for providing portable information is a head-mounted display (HMD) system. A head-mounted display system is a type of head-worn display system that uses a visor, a helmet, a goggle, or other head worn mount to place a display in front of one or both eyes. Typically, the head-mounted display includes a semi-transparent optical combining element upon which the display symbology is presented. The source of the symbology may be a liquid crystal display (LCD), liquid crystal on silicon (LCoS) display, or organic light emitting diode (OLED) display. The combining element allows the information presented on the HMD display to be superimposed on the visible scene and change as the vehicle operator moves his/her head around. Because this HMD system is head worn, there are some distinctive human body and vision system coupling characteristics that are preferably addressed. One of those is the human vestibulo-ocular reflex (VOR).
The normal VOR response is a compensatory eye movement that counters head movement when the human neural system detects motion of the head in space. For instance, rotating the head on horizontal plane to the right will induce the eye rotating left relative to the head coordinate frame to stabilize the visual axis of the gaze and keep the image fixed on the retina during the head motion. Moreover, this eye motion due to the VOR is not an exact inverse of the head motion due to the dynamic effects from the neural sensors and oculomotor nucleus response.
In current practice of HMD devices with synthetic vision image processing, images are usually compensated for the sensed head motion without dynamic compensation of the eye VOR effects. That is, the displayed image is shifted to reflect that the eye gaze is changing the direction when head moves and the eye gaze is usually assumed aligned the same as the head facing direction in the current practice of HMD design. In reality, the eye motion due to the involuntary vestibulo-ocular reflex is not aligned with the head motion, nor is it aligned with the pure inverse of the head motion. Without dynamically compensating the eye VOR effects, the resulting images may be unreadable to the human operator in a vibrating environment, such as operation of the vehicle over uneven terrain, or operation of an aircraft in a turbulent environment.
Therefore, it would be desirable to incorporate the eye VOR compensation to enhance the performance of the image stabilization and tracking design on an HMD device, especially when used in a high vibration environment. Furthermore, other desirable features and characteristics of the exemplary embodiments will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. Thus, it will be appreciated that even though the exemplary applications utilizing the VOR compensation in this disclosure are related to head-mounted display systems, this disclosure can be applied to any image display system used in a high vibration or changing environment by incorporating the VOR compensation in the image processing to enhance the cognition of the display information.